The present invention relates to an apparatus and method for controlling a heater provided in a gas concentration sensor for promoting activation of the gas concentration sensor.
Recently, there has been a demand for air-fuel ratio control for a vehicle-mounted engine, having enhanced control accuracy and lean mixture combustion in the engine. To meet those demands, a linear air-fuel ratio sensor (an oxygen responsive limit-current type A/F sensor) is used for detecting air-fuel ratio of air-fuel mixture gas supplied to the engine linearly over a wide air-fuel ratio zone. It is necessary to maintain the temperature of the sensor to a predetermined activation temperature in order to detect the air-fuel ratio (concentration of oxygen in exhaust gas) with high accuracy. For this purpose, the sensor is generally provided with a heater. The heater is controlled by an electric power supply control or by a feedback control for maintaining the heater temperature at a predetermined sensor activation temperature.
However, in the above heater control, it is likely that a heater abnormality is detected erroneously during operation of the sensor by an electric noise or a temporary electrical disconnection even while the heater control is the performed normally. Stopping the heater control in response to the detection of the heater abnormality will disable the air-fuel ratio feedback control using a highly accurate output signal of the sensor. Thus, it is necessary to restore the heater control to the normal operation when the abnormality of heater is temporary.